You apply the CompositionAttribute to a property that represents an association between two entities that are conceptually part of a hierarchy, such as a SalesOrderHeader entity and a SalesOrderDetail entity. These related entities are known as a compositional hierarchy. After defining the compositional hierarchy between the classes, you can perform data modification operations on the entities as a single unit instead of as separate entities. This simplifies middle-tier logic because you can write application logic for the entire hierarchy instead of splitting that logic into each entity and attempting to coordinate that split logic during data operations. For more information, see Compositional Hierarchies.